New to Istanbul

Hello everyone,
new to internations and Istanbul. Great to see such a supportive group in Istanbul.
I am residing near Beykoz and have time free between 8am and 3pm. I will have a day off a week but have no choice when this happens. Keen to connect with people in my area and central Istanbul.
I would like to find a good Turkish bath either central or in my area. Can anyone recommend ?
Getting Turkish sim card for iphone what would you recommend?
About visas what is the difference between resident visa and working visa?
A link to transport site in English please.
Any good website like gumtree for Istanbul in English.
Thanks in advance for all your support.
Megan